Lightning arrester



Oct 12, 1943- H. o. sToELTlNG LIGHTNING ARRESTER Filed Sept. 9, 1940 H iZ 7 9 R. Y

5 4. o 4 WM/ M WMNWWWWMQE a n i v V AMI Patented Oct. 12, 1943 LIGHTNINGARRESTER Herman O. Stoelting', Milwaukee, Wis., assignor to LineMaterial Company, Milwaukee, Wis., a corporation of Delaware ApplicationSeptember 9, 1940, Serial No. 355,954

Claims.

A lightning arrester for the protection of high voltage power linescustomarily includes a spark gap in series with a resistor-which latterusually is a so-called valve element consisting of a mass of comminutedsilicon carbide having characteristics which render it relatively highlyconductive when subjected to surge voltages such aslightning'discharges, but at the same time highly resistive atrelatively low voltages such as those employed in the transmission ofelectric power. A lightning arrester so constituted provides arelatively low impedance path to ground for destructive surges, butoperates promptly to interrupt the flow to ground of power current whichwould otherwise follow in the path ofv the surge current, once the sparkgap barrier is broken down.

One of the difficult problems encountered in I the development ofefficient lightning arresters has been that of overcoming so-calledflashovers-which expression pertains to the phenomenon of lightningashes and follow-through power current bridging the resistor elementalong the surface thereof-thus effectively nullifying the resistorelement as a means of suppressing power current flow and, in manyinstances, causing fracture or shattering of the glass or porcelainhousing.

Generally, if not always, the spark gap and resistor or valve element ofa lightning arrester is hermetically sealed within a housing of glass orporcelain and I have previously discovered that flash-overs can almostcompletely be prevented by bonding together the comminuted resistormaterial with a binder of sodium silicate and forming a firm sodiumsilicate bond between the resistor element and the interior of thehousingthe sodium silicate binder being substantially desiccated bybaking after assembly. A lightning arrester of that character may haveeither a porcelain or glass housing, but it has been found that althoughwith porcelain housings the sodium silicate bond between resistor andhousing is perfect, almost without exception, such is not the case whereglass housings are concerned. In the latter instance the sodium silicatebond between resistor element and housing ruptures in about of thearresters, upon being taken from the oven-due, no doubt, to differencein degree or rate of contraction on cooling and to the unavailability ofa cheap enough glass having properties by virtue of which rupturing ofthe bond might be avoidable. A loss of that magnitude is of courseintolerable and would to a considerable `extent spell commercialimpracticability of large glass housed arresters if the flashoverproblem could not otherwise be solved.

The primary object of the present invention is to obviate flashover bymeans applicable to lightning arresters having either porcelain or glasshousings and, particularly, to render more feasible the use of glasshousings by making it unnecessary to provide a bond between the resistorelement and the interior of the housingthus circumventing theaforementioned production losses resulting from bond ruptures-and,further, to accomplish that end without giving rise to excessive currentdensity in any part of the resistor element such as would be apt tocause clinkering of the valve material and sequential ineffectivenessthereof with respect to interruption of power current through thearrester.

The resistor element of a lightning arrester, consisting usually of amass of comminuted silicon carbide, must have a cross-sectional arealarge enough to ensure that the current density therethrough along anypath will not be apt to attain a magnitude sufficient to cause sinteringof the granules of silicon carbide or other transformation consequentupon excessive heating, which would render such path permanently soconductive as to prevent proper functioning of the resistor elementthereafter.

Such a resistor element can reasonably be considered as consisting of avery large number of electrically parallel conductive paths and it isconvenient so to regard it for the purposes of this specification, eventhough it probably is not true that such paths exist as individualclearly defined entities comparable, for example, to the individuallyinsulated conductors of a cable. If such individual paths, extendingfrom end to end of the resistor element, be assumed-and they are hereassumedit will be apparent that the conductivity of all the paths shouldbe of the same order if there is to be achieved something approaching auniform current density. Otherwise, a major part of the total currentmight be restricted to a relatively small part of the crosssectionalarea of the resistor, and excessive localized heating might occur withattendant formation of a clinker chain and resultant failure of thearrester. On the contrary, the present invention is predicated, intheory at least, upon bringing about a limited degree of non-uniformityin the conductivity of the several paths; but that non-uniformity,although apparently essential, must not be carried to excess because todo so would result, as above stated, in too much concentration ofthecurrent flowy in paths of constricted cross-sectional area.

I A. theoretical consideration underlying the present invention is thatby diverting the current ilow through the resistor element as much aspracticable away from the longitudinal exterior surfacev thereof the.tendency for iiashovers to occur is somewhat proportionately diminished;and with a View to achieving that end it was contemplatedthat theconductivity of the current paths running along and close to thelongitudinal axis .of the resistor should be greater than theconductivity of the paths at and adjacent the longitudinal exteriorsurface of the resistor, and that the paths intermediate of thelongitudinal axis and the exterior surface should be of graduatedintermediate conductivity. In addition, it was conceived that presentlythe most practicable way to realization of the aforementionedaccomplishment, on a commercial scale,- was to interpose in the resistorelement, at one or more points bintermediate of its length, portionsof'relatively high conductivity, so proportioned and so placed would beof maximum conductivity whereas the remaining paths would becharacterized by conductivity somewhat inversely proportional to theirdistances from the longitudinal axis. More speciiically, the inventiveconcept comprehends embedding and enveloping in the resistor one or moreor several pieces of metal of various lengths so placed as to producethe above, described result. v

In practice there need generally be provided only one slug of metal ofsuitable proportions and this ordinarily is embedded and enveloped inthe mass of comminuted material at a point .approximately midway of itslength. Such is :probably the most convenient way of carrying out theinvention, and it seems most expedient to make the metal slug oflenticular form; but it will be self-evident to those who comprehend the.inderlying principle of operation that the invention is susceptible ofa variety of embodiments.

In the drawing:

Fig. 1 is a View in side elevation, partly in section, showing animproved lightning arrester.

f Fig. 2 is a top plan view of a surge directing element.

Fig. 3 is a tcp plan view of the lower lightning arrester electrode.

Figs. 4 and 5 are fragmentary sectional views illustrating modicationsof the lightning arrester shown in Fig. 1.

Fig. 6 is an elevational view on a reduced scale, partly in section,illustrating a further modification of the lightning arrester shown inFig. 1.

The arrester shown in Fig. 1 comprises a housing I made of glass,porcelain or any other suitable insulating material. It may be notedthat the glass housing I is made up of a number of housing units joinedtogether in any convenient manner as by welding at 2 and 3. It may befurther noted that the bore of the housing is not uniform due to thewelds at 2 and 3. Housings may also be provided having a uniform boreand made as a single unit.

It is necessary to provide a relatively long housing, as shown, whendesigning an arrester adapted to operate on a comparatively high voltageelectric transmission system.

The lower end of the housing I apertured at 4 and having a dependingskirt portion is provided with a disc-like terminal member 8 notched at1 to receive a holding tool, not shown, and threadedly apertured at 6 toreceive the bolt portion l of the gap device Ill. The gap device III ismore fully disclosed in the application ot Ralph H. Earle, Serial Number269,065, iiled April 21, 1939,

- for Isolator.

The terminal 6 is provided at the upper side with a convex contactsurface I I and at the under side with a flat surface which seatsagainst an asbestos gasket I2. The gap device III is tightened into theterminal 6 and seated against a sealing gasket I3, thereby sealing thelower end of the housing against moisture.

An insulating compound I5 is placed within the depending skirt portion 6and around the gap device I6 to provide a further moisture seal for thehousing.

A properly prepared valve material I6, commonly comprising siliconcarbide or any other suitable material, is placed within the housing Iapproximately level with the ilrst weld at 2.

At this point in the iilling operation a lenticular conductive disc Ilhaving upper and lower convex surfaces I8 and I9 respectively iscentered within the housing I in contact with the valve material I6 forpurposes hereinafter described.

Additional valve material I6 is filled in around the disc I'I and withina predetermined distance from the upper end of the housing I.

It may be noted that the upper end of the column of valve material I6 issprayed with a illm of copper, not shown, in a well known manner and isrecessed a short distance at 20 to facilitate centering the spark gap 2|commonly used on lightning arresters of this type. The spark gapcomprises a pair of spaced parallel ceramic supports 22 supporting anumber of spaced cylindrical electrodes 23, the lower one of which isconnected by a screw, not shown, to the electrode disc 24 which seatsagainst the copper iilm within the recess 20.

The upper end of the housing I` is sealed against moisture by means of acap 25 in a manner more fully described in the above noted application.

The arrester is connected to an electric circuit by connecting a lineconductor, not shown, to the conductor 25 which is electricallyconnected to the spark gap 2I; and connecting a ground Wire, not shown,to the gap device I0 at 2l. When a lightning surge or other overvoltagecondition exists on the system connected at 26, the spark gap breaksdown electrically and the valve material I6 assumes a low resistance,thereby allowing the surge current to pass through the valve material I6between the upper electrode 24 and the lower electrode 6 through the gapdevice I0 to ground.

By providing the lenticular electrode I1 intermediate the electrodes 24and 6 and adjacent the constricted portion of the housing at the weld 2,the surge current passing through the valve material seeks paths awayfrom the wall of the housing and centrally of the electrode Il. This isobserved by noting that a shorter distance is provided in a pathextending between the central portions of the electrodes 6 and Il, andthe central portion of the electrode Il and the electrode 24 than isprovided between the peripheral surfaces of the electrodes adjacent thehousing.

The mass of valve material I6, together with the lenticular disc Ilembedded and and enveloped therein, constitutes an elongated conductive'medium electrically interconnecting upper electrode 24 with lowerelectrode 6; and it may for all practical purposes be considered thatthe aforementioned conductive medium presents a large number ofelectrically parallel conductive paths bridging the space between saidelectrodes. Manifestly. those paths are not clearly dened isolatedentities, but the effect apparently is the same as if such were thefact, and it will serve well, for purposes of description and claimterminology, to assume the presence of many individual geometricallyparallel conductive paths extending longitudinally through theconductive medium and distributed uniformly throughout the cross sectionthereof. Assuming absence of the lenticular disc, the aforementionedpaths would, for the most part, be of substantially equal conductivityand it follows that the current density`through the conductive mediumwould be substantially uniform. Such is the condition which obtains inlightning arresters of the prior art wherein many failures have in thepast been experienced due to flashovers occurring along the innersurface of the housing bore.

As stated at the beginning of this specification, I have been able,practically, to overcome flashover troubles by mixing the comminutedsilicon carbide with sodium silicate (water glass) and bonding the massto the inside of the housing with sodium silicate as ,a bonding agentthewet mass of silicon carbide and sodium silicate binder being baked untilsubstantially desiccate and solid. And, as previously indicated, thatmethod is applicable to both porcelain and glass housed arresters, butit is commercially uneconomical at present with respect to large glasshousings because of excessive production losses -due to unavailabilityof a glass which is both sufficiently cheap and capable of preventingrupture of the bond during the cooling off period after baking.

According to one theory which I have adopted as a plausible explanationof the operativeness of the present invention, the lenticular disc I1introduces a suiicient differentiation in the conductivity of theseveral parallel paths extending longitudinally through the conductivemedium to cause the current ilow therethrough to tend toward thelongitudinal axis. That is to say, the paths along and near the axis areof slightly greater conductivity than the paths more remote from theaxis-and particularly the paths closely adjacent the inner surface ofthe housing where destructive ashovers are prone to occur; and itfollows that there would be, in consequence, a greater current densityalong the axis of the conductive medium than at points remote therefrom.If the foregoing theory is correct, it is obvious that there is nothingparticularly critical about the shape of disc l1 so long as it isappropriately designed to create a suitable degree of concentration ofcurrent along the axis and a concomitant diversion of current away fromthe inner surface of the housing.

According to another plausible explanation, direct current conductivityand slight differences of direct current conductivity have little or nobearing on the operation of the lenticular disc so far as prevention offlashovers is concerned because what is being dealt with primarily ishigh voltage, high frequency lightning flashes which are attracted toand concentrate upon the conductor which is closest to the point oforigin and included in an easy path to ground-subject to the exceptionthat lightning will strike a pointed conductor, such as the tip of alightning rod, in

preference to an unpoint-ed conductive surface.

Fig. 4 shows fragmentarily an arrester similar to the one described withreference to Fig. 1, but showing the upper end of the valve material IBprovided with a disc-like electrode 28 having a convex contact surface29 embedded a predetermined distance into the valve material, and a ilatcontact surface 30 against which the electrode 24 of the spark gap 2lmakes electrical contact. A disc-like electrode 3| is embedded in thevalve material adjacent the weld 2 for reasons cited in reference toFig. 1.

It may be noted that in providing the upper end of the valve material I6with an electrode curved in a manner similar to the electrodes 6 and I1,the surge current is directed centrally of the valve material and awayfrom the housing in a positive manner.

Fig. 5 shows an arrester comprising a housing 32 made of porcelain orother suitable insulating material and having a uniform bore throughoutits length. Intermediate portions of the arrester are cut away,indicating that the housing may be provided in any predetermined length,depending upon the voltage under which the arrester is to operate.

The lower end of the housing 32 is provided with a circular electrode33, an anchor nut 34 mounted against the electrode 33 and a sealingwasher 35 positioned about the electrode. A lead alloy '36 is pouredaround the nut 34 within the sealing washer 35. The peripheral portionof the alloy is forced outwardly at 31, against the washer 35 by meansof a circular wedging tool, not shown, thereby providing a positivemoisture seal. The gap device l0 is secured to the nut 34 by means of abolt 38 and the housing further sealed against moisture by a sealingcompound 39.

A disc-like electrode 40 curved at the upper side to provide a convexcontact surface 4I is mounted against the electrode 33 and apredetermined amount of valve material I6 is packed within the housingand around the electrode 40 as shown. A disclike electrode 42 havin-gupper and lower convex surfaces 43 is embedded centrally andintermediate the ends of the valve ma terial I6 for reasons describedwith reference to the electrode I1 in Fig. 1. A disc-like electrode 44provided with a convex contact surface 45 is embedded in the valvematerial adjacent the upper end thereof. An electrode 46 is positionedin contact against the electrode 44 and the spark gap 2|, mounted on theelectrode 46 as shown. The upper end of the housing 32 is sealed againstmoisture in the manner described with reference to Fig. 1.

It may be noted that a minimum conductive path is provided between thecentral portions of the electrodes 44, 42, and 40 and a maximum distanceestablished between the same electrodes adjacent the housing 32, therebycausing the surge current to seek paths centrally of the valve material,preventing current concentration adjacent the housing.

Fig. 6 shows an arrester having a housing 41 made of glass, or othersuitable material, formed, as shown, with the intermediate portion ofits length diametrically enlarged and gradually tapering ofi' inopposite directions toward the dia.- metrically smaller end portions 48and 49.

The lower end of the housing 41 is assembled with an electrode 50, thegap device l0, and the assembled parts sealed therein in the mannerdescribed with reference to Fig. 1.

A predetermined amount of valve material 5| is placed within the housingas shown and a spark gap 2| positioned on the upper end of the materialwhich is provided with a film of copper, not shown. It may be noted thatthe film of copper provides more uniform electrical contact between thespark gap 2| and the valve material 5|. The upper end of the housing issealed against moisture by means of the cap 25 in the manner describedwith reference to F18. 1.

A spherical electrode 52 may be embedded centrally of the valve materialas shown.

By providing the housing 41 in the manner l just described, a shorterconductive path is established between the spark gap and the electrode50 through the central portion of the valve material than is providedadjacent the housing. The electrode 52 further tends to direct the surgecurrent centrally of the valve material.

From the foregoing description it is apparent that the objects of thisinvention have been attained by providing for a lighting arrestercomprising a housing, a valve material, including conductive meansadapted to direct the flow of surge current through the arrester awayfrom the housing.

Further objects have been attained by providing a valve material formedin a predetermined manner, whereby a minimum distance between contactsurfaces is maintained centrally thereof.

I claim:

1. In a lightning arrester, a pair of spaced electrodes and an elongateconductive medium interconnecting said electrodes, said mediumcomprising principally a mass of comminuted non-metallic material, saidmedium also including a slug of highly conductive material embedded andenveloped in said comminuted material and situated intermediately ofsaid electrodes and remote from both said electrodes, said slug beingelectrically connected with said electrodes through said comminutedmaterial and not otherwise, and having opposite surfaces individually inface-to-face spaced relation to said electrodes respectively, at leastone of said surfaces being so shaped as to provide shortened electricalpaths through said comminuted material between its cio-operating one ofsaid electrodes and said slug along lines contiguous to the longitudinalaxis of said medium, the shortness of said shortened paths being sodistinguished by comparison with the lengths of other electrical pathsthrough said comminuted material between said co-operating electrode andsaid slug in shunt to said shortened paths and more remote from saidlon-gitudinal axis than said shortened paths, said conductive mediumaffording many parallel electrical paths between said electrode and saidslug in shunt to said shortened paths and of somewhat greater lengthsthan said shortened paths and more remote from said longitudinal axisthan said shortened paths, both said slug surfaces being so formed thatthe thickness of said slug, measured longitudinally of said medium, isgreatest along and contiguous to the longitudinal axis of said mediumand approximately a minimum at points most remote from said axis, saidthickness being graduated approximately in inverse proportion to thedistance from said lon-gitudinal axis of the points at which themeasurements of said thickness are taken.

2, In a lightning arrester, a housing of insulating material having anelongate bore, an elongate conductive medium occupying said bore andinterconnecting said electrodes, said conductive medium comprisingprincipally a mass of comminuted non-metallic conductive material and aslug of highly conductive material embedded and enveloped in saidcomminuted material at a point intermediate of said electrodes andremote from both said electrodes, said slug having opposite surfacesindividually in face-to-face spaced relation to said electrodesrespectively, at least one of said surfaces being convex and having aportion adjacent or coincident with the longitudinal axis of saidmedium, which portion is spaced least remotely from the electrode facingsaid convex surface.

3. In a lightning arrester, a housing of insulating material having anelongate bore, an elongate conductive medium occupying said bore andconsisting principally of valve material having the properties ofrelatively low impedance to high voltage surges in the nature oflightning and relatively high impedance to lower voltages of the ordercommonly employed for power transmission, a pair of spaced electrodescontacting respectively the extremities of said conductive medium, and ahighly conductive lenticular disc completely embedded and enclosed insaid conductive medium at an intermediate point therein remote from bothsaid electrodes, the opposite convex surfaces of said disc beingdisposed individually in spaced face-to-face relation with saidelectrodes respectively and individually.

4. In a lightning arrester, a housing of insulating material having anelongate bore, an elongate conductive medium occupying said bore andconsisting principally of valve material having the properties ofrelatively low impedance to high voltage surges in the nature oflightning and relatively high impedance to lower voltages of the ordercommonly employed for power transmission, a pair of spaced electrodescontacting respectively the extremities of said conductive medium, and ahighly conductive lenticular disc completely embedded and enveloped inand coaxial with said conductive medium, the opposite convex surfaces ofsaid disc being disposed individually in spaced face-to-face relationwith said electrodes respectively and individually, said disc beingsituated intermediately of and remote from both said electrodes.

5. In a lightning arrester, a pair of spaced electrodes and an elongateconductive medium interconnecting said electrodes, said mediumcomprising principally valve material having the properties ofrelatively low impedance to high voltage surges in the nature oflightning and relatively high impedance to lower voltages of the ordercommonly employed for power transmission, said medium also including aslug of highly conductive material embedded and enveloped in said valvematerial and situated intermediately of said electrodes and remote fromboth said electrodes, said slug being electrically connected with saidelectrodes through said valve material and not otherwise, and havingopposite surfaces individually in face-to-face spaced relation to saidelectrodes respectively, at least one of said surfaces being so shapedas to eiect shortened electrical paths through said valve materialbetween its co-operating one of said electrodes and said slug alonglines contiguous to the longitudinal axis of said medium, the shortnessof said shortened paths being so distinguished by comparison with thelengths of other electrical paths through said valve material betweensaid eooperating electrode and said slug in shunt to said shortenedpaths and more remote from said longitudinal axis than said shortenedpaths, said conductive medium affording many parallel electrical pathsbetween said electrode and said slug in shunt to said shortened pathsand of somewhat greater lengths than said shortened paths and moreremote from said longitudinal axis than said shortened paths, both saidslug surfaces being so formed that the thickness of said slug, measuredlongitudinally of said medium, is greatest along and contiguous to thelongitudinal axis of said medium and approximately a minimum at pointsmost remote from said axis, said thickness being graduated approximatelyin inverse proportion to the distance from said longitudinal axis of thepoints at which the measurements of said thickness are taken.

6. In a lightning arrester an elongate conductive medium having theproperties of relatively low impedance to high voltage surges in thenature of lightning and relatively high impedance to lower voltages ofthe order commonly employed for power transmission, a pair of spacedelectrodes individual to and contacting the respective ends of saidmedium, and a third electrode embedded within said medium and connectedwith said spaced electrodes via said medium and not otherwise, saidthird electrode being situated intermediately of and remotely from bothsaid spaced electrodes, said third electrode being enveloped entirelywithin and spaced, at all peripheral points thereon, a substantialdistance from the proximate external peripheral surface of said medium,but otherwise having an area, transversely of said medium, which issubstantially coextensive with the coplanar crosssectional area of saidmedium.

7. In a lightning arrester. an elongate conductive medium having theproperties of relatively low impedance to high voltage surges in thenature of lightning and relatively high impedance to lower voltages oi.'the order commonly employed for power transmission, a pair of spacedelectrodes individual to and contacting the respective ends of saidmedium, the contacting surface oi at least one of said electrodes beingconvexly protrudent toward the other, and a third electrode embeddedwithin said medium and connected with said spaced electrodes via saidmedium and not otherwise, said third electrode being situatedintermediately o! and remotely from both said spaced electrodes, saidthird electrode being enveloped entirely within and spaced, at allperipheral points thereon, a substantial distance from the proximateexternal peripheral surface of said medium, but otherwise having anarea, transversely of said medium, which is substantially coextensivewith the coplanar crosssectional area oi said medium. y

8. In a lightning arrester, an elongate conductive medium having theproperties of relatively low impedance to high voltage surges in thenature of lightning and relatively high impedance to lower voltages ofthe order commonly employed for power transmission, a pair of spacedelectrodes individual to and contacting the respective ends of saidmedium, the contacting surfaces of said electrodes each being convexlyprotrudent toward the other, and a third electrode embedded within saidmedium and connected with said spaced electrodes via said medium and nototherwise, said third electrode being situated intermediately of andremotely from both said spaced electrodes, said third electrode beingenveloped entirely within and spaced, at all peripheral points thereon,a substantial distance from the proximate external peripheral surface ofsaid medium, but otherwise having an area, transversely of said medium,which is substantially coextensive with the coplanar crosssectional areaof said medium.

9. In a lightning arrester, a housing having an elongate bore, anelongate conductive medium n occupying said bore and endued with theproperties of relatively low impedance to hi-gh voltage surges in thenature of lightning and relatively high impedance to lower voltages ofthe order commonly employed for power transmission, a pair of spacedelectrodes within said housing and contacting the two ends of saidconductive medium individually, said conductive medium beingcharacterized by somewhat greater lengthwise conductivity per unit ofcross-section along paths embraced Within the cross-sectionalmid-portion thereof than along paths outside said mid-portion andconstituting the cross-sectional peripheral portion thereof, theabove-specified greater conductivity being obtained by the interpositionof localized metal in said mid-portion, said metal being embedded withinand enveloped by said conductive medium and situated intermediately ofsaid spaced electrodes and remotely from both said electrodes, saidmedium being further characterlzed in that no path therethroughinterconnecting said electrodes is so conductively predominant overother parallel paths, unit for unit oi? cross-section, as to create acondition likely to give rise to excessive localized heating and clinkerformation.

10 Lightning arrester structure in accordance with claim 9 and furthercharacterized in that the interposed localized metal is so distributedcross-sectionally of the conductive medium that the lengthwiseconductivity of said medium is thereby caused to be of a maximum valuealong the center-most portions thereof and of approximately`proportionately decreased conductivity along portions displacedradially from said center-most portion, so that the current density atany cross-sectional portion of said medium is inversely related to thedistance of the last-mentioned portion from the longitudinal axis ofsaid medium.

HERMAN O. STOELTING.

